The present invention relates to an electric arc coating device having:
a chamber with a chamber wall for receiving the substrates to be coated, the chamber being evacuatable and optionally controllably fillable with a reaction gas or an inert gas;
cathodes connected within the chamber so as to be electrically insulated from the chamber and consumable by the electric arc and connected to a first direct current source;
a second direct current source having a higher voltage than the first direct current source, with the negative pole of the second direct current source connected to the substrates to be coated which are electrically insulated relative to the chamber, whereby the positive poles of the first and second direct current sources are connected to at least one first anode.
Electric arc coating devices of the aforementioned kind are essentially known from U.S. Pat. No. 3,793,179. Further developments have been reported in the publication VDI-Zeitschrift 129 (1987) No. 1, p. 89-94.
In order to ensure good adhesion of the coatings, usually consisting of zirconium nitride, applied with the electric arc coating method, before the proper coating process and after chemical cleaning processes performed outside of the coating device an especially intensive cleaning of the objects to be coated, so called substrates, is carried out in which the substrates are subjected to a bombardment with ions which result from the plasma produced by the electric arc discharge. This ionic bombardment serves also to heat the substrate to a suitable temperature for the coating process. It is however disadvantageous that especially during manufacturing of substrates with uneven mass distribution and geometry overheating or etching of individual portions of the substrate will occur. Furthermore, it cannot be entirely prevented that on the surface of the substrate, despite high negative voltages of up to 1,000 volts applied thereto, intermediate layers of essentially undefined compositions are formed. Furthermore, it is desired to prevent the inclusion of microscopic particles of the material consumed by the electric arc discharge which have not been converted to the plasma stage (so-called droplets) into the coating layer because the coating's appearance and roughness is disadvantageously influenced by these droplets.
It is therefore an object of the present invention to provide an electric arc coating device of the aforementioned kind in which the ionic cleaning and heating of the substrate does not occur directly through the ions of the plasma stream, but through a glow discharge which causes an increased degree of ionization of the gases used in this stage of the process.